mkfifo(3p)

1MKFIFO(P)                  POSIX Programmer's Manual                 MKFIFO(P)
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NAME

6       mkfifo - make a FIFO special file
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SYNOPSIS

9       #include <sys/stat.h>
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11       int mkfifo(const char *path, mode_t mode);
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DESCRIPTION

15       The mkfifo() function shall create a new FIFO special file named by the
16       pathname pointed to by path. The file permission bits of the  new  FIFO
17       shall  be  initialized from mode.  The file permission bits of the mode
18       argument shall be modified by the process' file creation mask.
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20       When bits in mode other than the file  permission  bits  are  set,  the
21       effect is implementation-defined.
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23       If  path  names  a  symbolic link, mkfifo() shall fail and set errno to
24       [EEXIST].
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26       The FIFO's user ID shall be set to the process' effective user ID.  The
27       FIFO's group ID shall be set to the group ID of the parent directory or
28       to the effective group ID of the process. Implementations shall provide
29       a  way  to initialize the FIFO's group ID to the group ID of the parent
30       directory. Implementations may, but need not,  provide  an  implementa‐
31       tion-defined  way  to  initialize  the FIFO's group ID to the effective
32       group ID of the calling process.
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34       Upon  successful  completion,  mkfifo()  shall  mark  for  update   the
35       st_atime, st_ctime, and st_mtime fields of the file. Also, the st_ctime
36       and st_mtime fields of the directory that contains the new entry  shall
37       be marked for update.
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RETURN VALUE

40       Upon successful completion, 0 shall be returned. Otherwise, -1 shall be
41       returned, no FIFO shall be created, and errno shall be set to  indicate
42       the error.
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ERRORS

45       The mkfifo() function shall fail if:
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47       EACCES A  component  of  the  path  prefix denies search permission, or
48              write permission is denied on the parent directory of  the  FIFO
49              to be created.
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51       EEXIST The named file already exists.
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53       ELOOP  A loop exists in symbolic links encountered during resolution of
54              the path argument.
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56       ENAMETOOLONG
57              The length of the path argument exceeds {PATH_MAX} or a pathname
58              component is longer than {NAME_MAX}.
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60       ENOENT A  component  of the path prefix specified by path does not name
61              an existing directory or path is an empty string.
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63       ENOSPC The directory that would contain the new file cannot be extended
64              or the file system is out of file-allocation resources.
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66       ENOTDIR
67              A component of the path prefix is not a directory.
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69       EROFS  The named file resides on a read-only file system.
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72       The mkfifo() function may fail if:
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74       ELOOP  More  than  {SYMLOOP_MAX} symbolic links were encountered during
75              resolution of the path argument.
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77       ENAMETOOLONG
78              As a result of encountering a symbolic link in resolution of the
79              path  argument,  the  length  of the substituted pathname string
80              exceeded {PATH_MAX}.
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83       The following sections are informative.
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EXAMPLES

86   Creating a FIFO File
87       The  following  example  shows  how  to  create  a  FIFO   file   named
88       /home/cnd/mod_done,  with  read/write  permissions  for owner, and with
89       read permissions for group and others.
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91
92              #include <sys/types.h>
93              #include <sys/stat.h>
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96              int status;
97              ...
98              status = mkfifo("/home/cnd/mod_done", S_IWUSR | S_IRUSR |
99                  S_IRGRP | S_IROTH);
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APPLICATION USAGE

102       None.
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RATIONALE

105       The syntax of this function is intended to maintain compatibility  with
106       historical implementations of mknod(). The latter function was included
107       in the 1984 /usr/group standard but only for use in creating FIFO  spe‐
108       cial  files.  The  mknod()  function  was  originally excluded from the
109       POSIX.1-1988 standard as implementation-defined and replaced by mkdir()
110       and  mkfifo().  The mknod() function is now included for alignment with
111       the Single UNIX Specification.
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113       The POSIX.1-1990 standard required that the group ID of a newly created
114       FIFO be set to the group ID of its parent directory or to the effective
115       group ID of the creating process. FIPS 151-2 required that  implementa‐
116       tions  provide a way to have the group ID be set to the group ID of the
117       containing directory, but did not prohibit  implementations  also  sup‐
118       porting a way to set the group ID to the effective group ID of the cre‐
119       ating process. Conforming applications should not assume which group ID
120       will  be used. If it matters, an application can use chown() to set the
121       group ID after the FIFO is created, or determine under what  conditions
122       the implementation will set the desired group ID.
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FUTURE DIRECTIONS

125       None.
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COPYRIGHT

132       Portions of this text are reprinted and reproduced in  electronic  form
133       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
134       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
135       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
136       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
137       event of any discrepancy between this version and the original IEEE and
138       The Open Group Standard, the original IEEE and The Open Group  Standard
139       is  the  referee document. The original Standard can be obtained online
140       at http://www.opengroup.org/unix/online.html .
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144IEEE/The Open Group                  2003                            MKFIFO(P)